Organoaluminoxanes are known in the art and can be produced by the partial hydrolysis of hydrocarbyl aluminum compounds. Such aluminoxanes have been found useful in a variety of chemical reactions, including utility as cocatalyst components for polymerization catalysts, especially in high activity metallocene catalyst systems. Such metallocene catalysts have been used in homogeneous solution polymerization. Since such homogeneous catalyst systems are soluble in the polymerization medium it is generally observed that the resulting polymer has low bulk density.
Attempts to use metallocene/organoaluminoxane catalyst systems in a slurry or particle form type polymerization have not heretofore been found to be commercially feasible. It has been observed that when such particle form polymerizations are carried out in the presence of a soluble metallocene/organoaluminoxane catalyst system, large amounts of polymeric material are formed on the surfaces of the polymerization vessel. This fouling produces an adverse effect on the heat transfer and also results in the need for periodic, if not continuous, cleaning of the reactor. It is therefore necessary to have a catalyst system which will not cause significant amounts of reactor fouling.
It is known that a solid form of organoaluminoxane can be obtained by treating a commercial organoaluminoxane solution with a countersolvent; however, such solids have been found to cause reactor fouling in slurry polymerizations. Reactor fouling is still a problem in slurry polymerization even when a countersolvent is used to precipitate the organoaluminoxane onto an insoluble particulate carrier.
It would therefore be desirable to produce an economical solid organoaluminoxy product useful as a cocatalyst in a polymerization process free of reactor fouling.